Cryogenic refrigerating system

ABSTRACT

The present invention provides a cryogenic refrigerating system for achieving ultra low temperature by sequentially obtaining low temperature through repetition of expansion and evaporation of a mixed-refrigerant in multiple stages. The refrigerating system includes a heat exchanger and a compressor between a final evaporator and a compressor. The heat exchanger causes evaporated refrigerant vapor in a suction tube for the compressor to be heated and to be drawn into the compressor, and causes the refrigerant condensed by a condenser to be supercooled. The refrigerating system includes a plurality of expansion/suction apparatuses connected with one another between the gas/liquid separator and the final evaporator.

TECHNICAL FIELD

The present invention relates to a multi-stage expansion/suction type ofcryogenic refrigerating system, wherein the Bernoulli's principle thatas the flow velocity of a fluid in a tube increases, pressure exerted bythe fluid in the tube decreases is applied to a refrigerating cyclesystem so that low temperature can be achieved in a refrigeratingchamber of a refrigerator by lowering temperature and pressure of arefrigerant in multiple stages when the refrigerant flows from a hightemperature side to a low temperature side.

More specifically, the present invention relates to a cryogenicrefrigerating system, wherein a specific refrigeration effect thereof isincreased only by one compressor in such a manner that a process oflowering pressure of a low-temperature side refrigerant by means ofstrong suction force in an evaporated refrigerant carrying tubegenerated when a liquid refrigerant is expanded and injected at a highvelocity toward an inlet of a double tube is repeatedly performed inmultiple stages, and thus, evaporation pressure of the refrigerant canbe maintained below suction pressure of the compressor and its stabilitycan be ensured even in case of continuous operation thereof.

BACKGROUND ART

Generally, ultra low temperature is needed for long-term preservation oftissue, cells or genes, a semiconductor fabricating process, anapparatus for inducing a superconductivity phenomenon, etc.Particularly, in case of biological materials such as cells, if they arekept at temperature of −130° C. or less that corresponds torecrystallization temperature of ice, water contained therein is notcrystallized but is in amorphous state. Thus, since it is not likelythat a cell membrane is destructed, the term of preservation thereforecan be greatly prolonged over 10 years. Although there are varioustechnologies for achieving such ultra low temperature, a method using avapor compression refrigeration cycle or liquid nitrogen is widely used.In order to achieve ultra low temperature of about −135° C. to −150° C.,it is necessary to employ a multi-stage cascade refrigerating cyclehaving three stages or more, or to use the liquid nitrogen havingliquefaction temperature of −196° C. However, since the liquid nitrogenis used up only once, it is necessary to refill the liquid nitrogen foranother use. Thus, its use is inconvenient and its operating cost isincreased. On the other hand, in case of the multi-stage cascaderefrigerating cycle, there is a problem in efficiently achieving thedesired ultra low temperature. In addition, there is another problem inthat an apparatus employing the multi-stage cascade refrigerating cycleis complex in its structure, and thus, failures of the apparatusfrequently occur and its operating cost is also increased.

In consideration of these problems, there has been proposed a cryogenicrefrigerator, which is disclosed in an article, entitled “Temperature inRefrigerating Chamber of Compressor-type Refrigerator” in NikkeiMechanical, No. 496 (Dec. 23, 1996), pp. 44-45, Japan. The cryogenicrefrigerator employs a two-stage cascade mixed-refrigerant refrigerationcircuit (i.e., a combination of a two-stage cascade refrigerationcircuit and a mixed-refrigerant circuit) for achieving lower temperaturein a low-temperature side refrigeration circuit by using ahigh-temperature side refrigeration circuit

In the two-stage cascade mixed-refrigerant refrigeration circuit,achievable temperature in a final evaporator is −155° C., andtemperature obtained in the refrigerating chamber is −152° C. Asschematically shown in FIG. 2, there are the two separate high- andlow-temperature side refrigeration circuits which in turn are connectedwith each other through a cascade condenser. The cascade condenserserves as an evaporator for the high-temperature side refrigerationcircuit and as a condenser for the low-temperature side refrigerationcircuit. The high-temperature side refrigeration circuit is used forachievement of further lower temperature in the low-temperature siderefrigeration circuit.

In particular, in order to achieve temperature of −100° C. or less, themixed-refrigerant refrigeration circuit was employed in the lowtemperature side. A typical refrigerant is a mixed-refrigerant comprisedof seven kinds of refrigerants such as R412A having evaporationtemperature of −40° C. for the high temperature side, and R508 (mixtureof R23 and R116) having evaporation temperature of −86° C., R22 havingevaporation temperature of −41° C., and R14 having evaporationtemperature of −128° C. for the low temperature side. Themixed-refrigerant goes through the respective stages to achieve the lowtemperature.

However, in the two-stage cascade mixed-refrigerant refrigerationcircuit, since two compressors are separately installed in therespective high- and low-temperature side refrigeration circuits,consumption of electric power is increased and the structure of therefrigeration cycle thereof is complicated. In addition, in order tomaintain the temperature in the refrigerating chamber at −152° C., it isnecessary to continuously operate the refrigerator. However, it isdifficult to operate continuously and stably the refrigerator sincethere is a problem in that residual oil which has been moved along withthe refrigerant from the compressor to a low pressure side is notcompletely collected into the compressor to cause the lubricating oil tolack on sliding surfaces in the compressor and consequently a cylinderof the compressor to get scorched and stuck. Moreover, there are alsoproblems in that suction pressure at low temperature is reduced andrefrigeration performance is reduced.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a refrigerating systemwhich ensures reliability of the equipment thereof by maintaining stableperformance even in case of continuous operation of the cryogenicrefrigerating system.

Another object of the present invention is to provide a refrigeratingsystem which improves life or reliability of the equipment thereof byensuring the smooth operation of a compressor.

A further object of the present invention is to provide a refrigeratingsystem which ensures external competitiveness of a product by enhancingthe refrigeration efficiency thereof over 20% and stabilizing theoperation thereof at ultra low temperature.

The above objects of the present invention can be achieved by amulti-stage expansion type of cryogenic refrigerating system, wherein aliquid refrigerant is expanded at an upper portion of an evaporatedrefrigerant carrying tube and is injected toward a downstream side withrespect to a flow direction of evaporated refrigerant vapor in multiplestages so as to strongly draw refrigerant vapor in the evaporatedrefrigerant carrying tube and thus to lower evaporation pressure of therefrigerant below suction pressure of a compressor. Since the evaporatedrefrigerant vapor is strongly drawn and urged at a high velocity, flowvelocity and pressure of the refrigerant vapor are increased and thesuction pressure of the compressor is maintained over predeterminedpressure. Accordingly, volumetric efficiency of the compressor can beimproved and residual oil in a refrigeration circuit can be completelyreturned to the compressor. According to the present invention, it ispossible to achieve final evaporation temperature of −160° C. andtemperature of a refrigerating chamber of −156° C.

Further, the above objects of the present invention can be achieved by amulti-stage mixed-refrigerant system comprising a compressor forcompressing a mixed-refrigerant; an oil separator for separating oilfrom the refrigerant compressed by the compressor, collecting theseparated oil into the compressor, and then discharging the refrigerant;a condenser for cooling the high-temperature and high-pressure gaseousrefrigerant discharged from the oil separator to liquefy the gaseousrefrigerant; a heat exchanger which is installed on an evaporatedrefrigerant carrying tube for directing evaporated refrigerant vapor tothe compressor in order to lower temperature of the condensed liquidrefrigerant and in which the condensed high-temperature liquidrefrigerant is caused to discharge heat therefrom to the evaporatedlow-temperature refrigerant vapor and to be supercooled, and therefrigerant flowed toward an inlet of the compressor is heated andevaporated; a gas/liquid separator for separating the condensedmixed-refrigerant passing through the heat exchanger into the liquidrefrigerant and the gaseous refrigerant; a plurality ofexpansion/suction apparatuses; and a final evaporator.

In the expansion/suction apparatus, the liquid refrigerant separated bythe gas/liquid separator sequentially passes through an expansion deviceinstalled in a tube, is injected from a nozzle provided on an end of thetube toward an outer tube for the evaporated refrigerant of a doubletube, is evaporated while flowing from an upstream side to thedownstream side, and communicates with an evaporated refrigerantcarrying tube on a high-temperature side. At this time, a throttlingphenomenon occurs in the vicinity of the nozzle and the refrigerantvapor in the evaporated refrigerant carrying tube is strongly drawn, sothat the drawn refrigerant vapor is caused to flow into the outer tubeof the double tube from the upstream side to the downstream side alongwith the injected refrigerant which has passed through the expansiondevice. At the same time, the residual oil contained in the refrigerantis moved toward the compressor, and an inner tube for the condensedrefrigerant disposed inwardly from the outer tube for the evaporatedrefrigerant of the double tube which has two concentric tubes ofdifferent diameters directs the gaseous refrigerant separated by thegas/liquid separator in an upward direction, so that the gaseousrefrigerant is condensed and the condensed refrigerant flows into agas/liquid separator on the low temperature side. In such way, theliquid refrigerant from the gas/liquid separator passes through theexpansion device and is injected from the nozzle, and then, the injectedrefrigerant is caused to flow together with the refrigerant vapor drawndue to the injection of the liquid refrigerant, toward the hightemperature side along an evaporated refrigerant carrying tube on thehigh temperature side which communicates with the double tube. Thegaseous refrigerant from the gas/liquid separator is condensed whileflowing upwardly through the inner tube for the condensed refrigerant ofthe double tube, and then flows into the gas/liquid separator on the lowtemperature side. In such way, the expansion/suction apparatusconstructs one cycle. The plurality of expansion/suction apparatuses areconnected with each other in multiple stages so that the expansion andcondensation of the refrigerant are repeated, thereby sequentiallyachieving low temperature.

In the final evaporator, condensed refrigerant which has passed througha final expansion/suction apparatus is condensed again in a heatexchanger disposed below the final evaporator, and flows into the finalevaporator through an expansion device. The refrigerant introduced intothe final evaporator is evaporated while flowing downwardly. Thecompletely evaporated refrigerant flows into an evaporated refrigerantcarrying tube of the final expansion/suction apparatus. Therefore, anintegrated circuit is formed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic circuit diagram of a cryogenic refrigeratingsystem according to the present invention.

FIG. 2 is a schematic circuit diagram of a cryogenic refrigeratingsystem according to the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

According to a preferred embodiment of the present invention, theaforementioned expansion/suction apparatuses are connected in fourserial stages between the heat exchanger on the high temperature side ofthe refrigerating system and the final evaporator on the ultra lowtemperature side thereof. In such a case, the refrigerant evaporatingtemperature became ultra low temperature of −160° C. (at this time, thetemperature in the refrigerating chamber became −156° C.).

Hereinafter, a preferred embodiment of the present invention will bedescribed in detail with reference to the accompanying drawings.However, it is merely intended to specifically illustrate the presentinvention to such an extent that a person having ordinary knowledge inthe art to which the present invention pertains can easily work thepresent invention. Accordingly, it should not be construed that thetechnical spirit and scope of the present invention are limited thereto.

As shown in FIG. 1, a cryogenic refrigerating system according to apreferred embodiment of the present invention comprises a compressor 1for compressing a mixed-refrigerant; a condenser 2 for liquefying hightemperature and high pressure refrigerant vapor compressed by thecompressor 1 (among the mixed-refrigerant, a refrigerant having a highboiling point is liquefied); and an oil separator 10 installed betweentubes for the compressor 1 and the condenser to separate oil from thecompressed refrigerant and return the oil to the compressor 1.

The cryogenic refrigerating system of the present invention furthercomprises a heat exchanger 3 which is installed between an evaporatedrefrigerant carrying tube 6 and a suction portion of the compressor 1,causes the refrigerant condensed in the condenser to be supercooled andflowed to a first gas/liquid separator 4 a, and causes refrigerant vaporto be heated for forming dry saturated vapor and moved to thecompressor; and a filter dryer 12 disposed between tubes for thecondenser 2 and the heat exchanger 3 for removing moisture and foreignmaterial contained in the refrigerant.

The cryogenic refrigerating system of the present invention furthercomprises the first gas/liquid separator 4 a for separating thecondensed mixed-refrigerant, which has passed through the heat exchanger3 and has been supercooled, into a liquid refrigerant and a gaseousrefrigerant, and a first expansion device 8 a for reducing the pressureof liquid refrigerant separated by the first separator 4 a to its ownevaporation pressure.

The refrigerant which has passed through the first expansion device 8 ais injected from an upstream side to a downstream side toward a doubletube communicating with the evaporated refrigerant carrying tube 6 a bymeans of a nozzle 7 a that is installed in a converging and divergingside end of a tube for the evaporated refrigerant located at a portioncommunicating with the evaporated refrigerant carrying tube 6 a. At thistime, a throttling phenomenon occurs due to the injection of therefrigerant, and thus, the pressure in the evaporated refrigerantcarrying tube 6 a is greatly reduced. Consequently, the refrigerantvapor in the evaporated refrigerant carrying tube 6 a is strongly drawn,and the refrigerant injected at a high speed through the first expansiondevice 8 a and the nozzle 7 a flows fast from the upstream side to thedownstream side along the tube for the evaporated refrigerant, i e anouter tube of the double tube, together with the drawn refrigerantvapor. Accordingly, a predetermined velocity of the refrigerant isensured, and perfect oil recovery is made since residual oil containedin the refrigerant moves toward the compressor. As a result, highefficiency and safety of the refrigerating system according to presentinvention is guaranteed. At the same time, the gaseous refrigerant fromthe first gas/liquid separator 4 a on the high temperature side of therefrigerating system is condensed while flowing upwardly along a tubefor the condensed refrigerant, and is then introduced into a gas/liquidseparator 4 b on the low temperature side of the refrigerating system.

Preferably, the expansion/suction apparatuses in which the gaseous andliquid refrigerants from the gas/liquid separator flow in the oppositedirections are repeatedly constructed in multiple stages toward the lowtemperature side of the refrigerating system.

That is, according to the preferred embodiment of the present invention,the expansion/suction apparatuses A to D, which are constructed in sucha manner that the evaporated refrigerant vapor flows toward the hightemperature side of the refrigerating system and the condensedrefrigerant liquid flows toward the low temperature side of therefrigerating system, are connected in series with one another. Thus,the temperature of the condensed refrigerant flowing out from theexpansion/suction apparatus becomes lower as the refrigerant advancestoward the low temperature side of the refrigerating system. Thecondensed refrigerant which has passed through the finalexpansion/suction apparatus D is condensed again in a heat exchanger 15,flows through a final expansion device 8 e, is introduced into an upperportion of a final evaporator 14, and then flows through the finalevaporator downwardly. At this time, the condensed refrigerant isevaporated and absorbs heat from the refrigerating chamber. Thus, theultra low temperature of −160° C. (temperature in the refrigeratingchamber: −160° C.) has been obtained. Since the completely evaporatedrefrigerant flows into an evaporated refrigerant carrying tube 6 d ofthe final expansion/suction apparatus through the outer tube of thedouble tube located below the evaporator 14, the cryogenic refrigeratingsystem with an integrated circuit formed therein is constructed.

The reference numeral 11, which has not yet been explained, denotes anexpansion tank for storing highly increased pressure produced at thetime of initial operation of the compressor 1; the reference numeral 13denotes a suction pressure regulating valve for performing overloadcontrol when the overload occurs at a suction portion of the compressor1; and the reference numerals 9 a to 9 d denote pressure gauges forindicating the pressure of the refrigerant flowing through the relevantevaporated refrigerant carrying tubes.

As described above, even though a multi-stage system in which theexpansion/suction apparatuses A to D are connected in series with oneanother in order to obtain the ultra low temperature of −160° C. isconstructed, there is still limitation on achievable ultra lowtemperature. Therefore, the present invention intends to employ arefrigerating system in which a mixed-refrigerant is used. Themixed-refrigerant in the expansion/suction apparatus complicatedlybehaves within the refrigeration circuit when the refrigerator actuallyoperates. The ultra low temperature is obtained according to theliquefaction/evaporation processes to be roughly described below.

Since the refrigeration circuit on the high temperature side of therefrigerating system is well known, the description thereof will beomitted. Thus, the operation of each expansion/suction apparatus on thelow temperature side of the refrigerating system will be describedbelow.

In the expansion/suction apparatus A, the liquid refrigerant R-600A fromthe first gas/liquid separator 4 a is evaporated. At this time, thepressure of the evaporated refrigerant in the evaporated refrigerantcarrying tube 6 a is approximately −18 cmHg, and the temperature of therefrigerant flowing through the injection nozzle 7 a is approximately−62° C.

In the expansion/suction apparatus B, the liquid refrigerants R-22,R-290 from the gas/liquid separator 4 b of the expansion/suctionapparatus A are evaporated. At this time, the pressure of the evaporatedrefrigerant in the evaporated refrigerant carrying tube 6 b isapproximately −28 cmHg, and the temperature of the refrigerant flowingthrough the injection nozzle 7 b is approximately −119° C.

In the expansion/suction apparatus C, the liquid refrigerants R-116,R-23 from the gas/liquid separator 4 c of the expansion/suctionapparatus B are evaporated. At this time, the pressure of the evaporatedrefrigerant in the evaporated refrigerant carrying tube 6 c isapproximately −35 cmHg, the temperature of the refrigerant flowingthrough the injection nozzle 7 c is approximately −136° C., and thetemperature of the refrigerant heat-exchanged at the double tube 5 c isapproximately around −128° C.

In the expansion/suction apparatus D, the liquid refrigerants R-1150,R-14 from the gas/liquid separator 4 d of the expansion/suctionapparatus C are evaporated. At this time, the pressure of the evaporatedrefrigerant in the evaporated refrigerant carrying tube 6 d isapproximately −45 cmHg, the temperature of the refrigerant flowingthrough the injection nozzle 7 d is approximately −152° C., and thetemperature of the refrigerant which has heat-exchanged at the doubletube 5 d is about −147° C.

The refrigerant that will be evaporated in the final evaporator 14 is aliquid refrigerant R-50 (in which He, Ar, or the like can be added) fromthe expansion/suction apparatus D. The refrigerant is supercooled againwhile flowing through the heat exchanger 15 made of the double tube andlocated below the final evaporator. Thus, the temperature of therefrigerant becomes −153° C. Thereafter, the evaporated refrigerant isintroduced into the evaporator via the expansion device 8 e. At thistime, the temperature of the refrigerant at an inlet of the evaporator14 is −160° C., and the temperature of the refrigerant at an outlet ofthe evaporator is −154° C. Accordingly, the ultra low temperature of−156° C. is obtained as a temperature within the refrigerating chamber.

Further, when the refrigerant separated by the relevant separator isinjected from each of the injection nozzles 7 a to 7 d at the relevantstage, the Bernoulli's principle is applied to a process of drawing theevaporated refrigerant vapor from each of the evaporated refrigerantcarrying tubes 6 a to 6 d, and expanding and transferring the injectedrefrigerant together with the drawn refrigerant toward each of thedouble tubes 5 a to 5 d. Thus, the suction pressure of the compressorbecomes as strong as the pressure value of each of the pressure gauges 9a to 9 d installed on the evaporated refrigerant carrying tubes.Accordingly, the problems that the refrigerant evaporating temperatureis increased and refrigeration performance is reduced due to reductionof the suction pressure are overcome.

Industrial Applicability

As described above, according to the present invention, the evaporationpressure of the refrigerant is kept below the suction pressure of thecompressor of the refrigerator, and thus, the stable performance of therefrigerating system can be maintained even in case of continuousoperation of the refrigerating system under the maximum temperaturecondition.

Further, the pressure and the flow velocity of the refrigerant drawntoward the high pressure side can be increased at the respective stagesby using the throttling phenomenon, so that the residual oil on the lowpressure side can be completely collected into the compressor. Thus, thesmooth operation of the compressor can be ensured and the usable lifeand reliability of the equipment of the refrigerating system can beimproved.

Moreover, since the liquid refrigerant is injected from the nozzletoward the end of the evaporated refrigerant carrying tube, thethrottling phenomenon occurs. The suction force generated as suchstrongly draws upwardly the refrigerant vapor, and thus, the stable flowof the refrigerant can be obtained. Consequently, the usable life of theequipment is prolonged, and at the same time, the refrigerationefficiency can be improved over 20% in the art.

According to the present invention, there is an advantage in that themulti-stage expansion compressor type refrigerator can be continuouslyand stably maintained at the temperature of −156° C.

What is claimed is:
 1. A multi-stage mixed-refrigerant type cryogenicrefrigerating system including a compressor (1) for compressing amixed-refrigerant drawn thereinto, an oil separator (10) for separatingoil contained in the refrigerant compressed by the compressor, acondenser (2) for liquefying refrigerant vapor discharged from the oilseparator, a heat exchanger (3) for heating evaporated refrigerant vaporintroduced after circulating through a low-temperature siderefrigeration cycle to be further evaporated and for supercooling therefrigerant condensed by the condenser (2), a first gas/liquid separator(4 a) for separating the supercooled mixed-refrigerant into a liquidrefrigerant and a gaseous refrigerant, and a final evaporator forevaporating the refrigerant to be returned to the compressor (1), therefrigerating system further comprising: a plurality ofexpansion/suction apparatuses connected with one another in series,wherein each expansion/suction apparatus is constructed such that aliquid mixed-refrigerant from the first gas/liquid separator (4 a)passes through an expansion device (8 a) and is then injected from aninjection nozzle (7 a) installed on a side end of an evaporatedrefrigerant carrying tube (6 a) into an outer tube of a double tube sothat the injected refrigerant is evaporated while flowing downwardly andthen flows into an evaporated refrigerant carrying tube (6) on a hightemperature side, and a gaseous mixed-refrigerant discharged from thefirst gas/liquid separator (4 a) flows upwardly through an inner tubefor the condensed refrigerant of the double tube (5 a) to be condensedand is then introduced into a second gas/liquid separator (4 b); andwherein the refrigerant condensed by passing through a finalexpansion/suction apparatus D is introduced into a fifth expansiondevice (8 e) through a heat exchanger disposed below the finalevaporator, the refrigerant introduced into the evaporator (14) isevaporated, and the completely evaporated refrigerant is returned to thecompressor (1) through a tube for the evaporated refrigerantcommunicating with the evaporated refrigerant carrying tube, whereby arefrigerant circuit of the refrigerating system is formed.
 2. Thecryogenic refrigerating system as claimed in claim 1, wherein fourexpansion/suction apparatuses are connected with one another in seriesbetween the heat exchanger on the high temperature side and theevaporator on an ultra low temperature side.
 3. The cryogenicrefrigerating system as claimed in claim 1, wherein the injection nozzleis installed at a narrow end of the tube for the evaporated refrigerantcommunicating with the evaporated refrigerant carrying tube.